Removal Of N-Methylpyrrolidone Hydrogen Bonded To Polyanilina Free-Standing Films By Protonation-Deprotonation Cycles

PONZIO, E.A.; ECHEVARRIA, R.; MORALES, G.M.; BARBERO, C.

POLYMER INTERNATIONAL

John Wiley & Sons Ltd. - Society of Chemical Industry

Año: 2001 vol. 51 p. 1180 - 1185

0959-8103

Free-standing films of polyaniline (PANI), in an emeraldine base state, prepared by evaporation of polymer solutions in N-methylpyrrolidone (NMP) retain solvent even under dynamic vacuum drying as indicated by transmission Fourier transform infrared (FTIR) spectroscopy, where a band at 1670 cm-1 is clearly observed. Upon protonation-deprotonation cycles in aqueous media the weight of the dry base film decreases indicating gradual loss of NMP. Transmission FTIR spectra shows also the washing out of NMP with a clear decrease in intensity of the hydrogen-bonded >C=0 stretching band (1670 cm-1) of NMP. During this process the bands between 3500 and 3200 cm-1, assigned to >N-H stretching in the PANI backbone, change intensity suggesting that intermolecular hydrogen-bonded >N-H, with carbonyl oxygen of NMP, is replaced by free >N-H. This is clear evidence of specific interaction of NMP with the emeraldine base. A similar loss of NMP is observed during heating but evidence of polymer degradation is also present. A mechanism is proposed to account for the loss of hydrogen-bonding ability upon protonation which requires delocalization of the radical cations in the protonated films. © 2001 Society of Chemical Industry.